Smart Devices have to be tested using an "Open Loop" rather than a "Closed Loop" test. Conceptually, open loop tests can be slightly more challenging because the test procedures have a couple of steps more than in closed loop tests. Also, not all commercially-available analyzers are capable of testing open loops.
Fortunately, the NTi Audio Smart Device Testing solution ensures that open loop testing is not a challenge at all.
For your interest and understanding, we now discuss the difference between open and closed loop testing:
A Closed Loop Loudspeaker Test
A loudspeaker test is defined as being "closed" when the generator is connected directly to the loudspeaker under test. Therefore, in a Closed Loop loudspeaker test, we connect the sound generator directly to the wires at the back of the loudspeaker under test and play the test signal. The response of the loudspeaker to this test signal is measured with a measurement microphone, and recorded by the analyzer.
A Closed Loop Microphone Test
Similarly in a Closed Loop microphone test, the analyzer is connected directly to the wires on the back of the microphone under test. We play the test signal through a calibrated loudspeaker, and the response of the microphone is recorded by the analyzer.
An Open Loop Loudspeaker Test
For a loudspeaker test on the Amazon Echo, we have no direct physical access to the back of the loudspeaker in the Echo itself (without destroying the Echo). The test signal is fetched by Alexa from the Amazon Cloud. As the generator is thus not connected directly to the loudspeaker under test, we have what is considered to be an Open Loop loudspeaker test.
An Open Loop Microphone Test
To test the microphone array in the Amazon Echo, we also have no direct physical access to the back of the microphones in the Echo itself (again without destroying the Echo). The signal recorded by the Echo microphones is stored on the Amazon Cloud and played back manually to the Analyzer. As the analyzer is not connected directly to the microphones under test, we have what is considered to be an Open Loop microphone test.